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Thread: ATC200 1984 Refuses to Start, Low Compression

  1. #1
    Join Date
    Jul 2018
    Location
    PA
    --
    29

    ATC200 1984 Refuses to Start, Low Compression

    After months of this baby sitting and replacing everything imaginable electrical it still will not start.

    Just did top end new gaskets, piston, rings, camshaft
    NEW: pulse generator, extra CDI, air filter, Spark plug, Ignition Coil, Stator Coil
    Rebored cylinder
    Adjusted valves slightly so not ticking but not sure if correct

    Result:
    Compression still @ 30psi will not start does not even sound like there is spark but
    electrical meter testing seems fine

    Valves the issues??? Timing???

  2. #2
    Join Date
    Jul 2018
    Location
    TN
    --
    1,065
    If you have the right size piston and rings in a freshly bored cylinder then your issue is most likely a valve. Valves are pretty cheap. I've replaced (and lapped in) them in every rebuild I have done so far. You could have the perfect ring gap and the highest compression piston imaginable and if the valves aren't sealing....it's crapola.
    It's sounds insulting but it's been done MANY times...you sure the right size piston and rings are in there? If so, pull that head and rework it, then a new base and head gasket.
    I was born and raised on Venus & I may be here a while.....

  3. #3
    Join Date
    May 2015
    Location
    San Diego, CA
    --
    1,738
    Let's forget about anything electrical and deal with the 30 psi compression.

    Gabriel is correct....it's probably valves. I would say do the oil trick to see if it's valves or rings but since it's 30 psi it needs to come apart anyways so focus on the head and valves. Put gas in the valve area and see if any seeps through. Make sure valves don't look pitted in the seat area. Also make sure cam timing is correct. Do it slow and methodically so nothing gets overlooked.

    You got this...just take your time. Good luck

  4. #4
    Join Date
    Jul 2018
    Location
    TN
    --
    1,065
    Anality during assembly prevents feeling like an azz when it won't start.
    I was born and raised on Venus & I may be here a while.....

  5. #5
    Join Date
    Jul 2018
    Location
    PA
    --
    29
    Thanks for the input definetly right size piston and gaskets, The valves was literally my last thought since it was the only thing i did not service. Let me pull it apart AGAIN and take a look they looked fine to me but idk anymore.

    For cam timing the timing chain mark and upper cam sprocket have to be aligned correct?

  6. #6
    Join Date
    Jul 2018
    Location
    TN
    --
    1,065
    Quote Originally Posted by dwheeler23 View Post
    For cam timing the timing chain mark and upper cam sprocket have to be aligned correct?
    Sort of. Those marks line up more than once in 4 cycles.

    Rotate the engine to top dead center, make sure the flywheel mark is aligned. THEN move the cam to install the sprocket with those marks aligned.
    Getting that wrong; Best case scenario, it don't run.....worst case you crater a piston into a valve. That will suck very much bad.
    I was born and raised on Venus & I may be here a while.....

  7. #7
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    Tell me how you set the valve clearance.

    "not ticking" well... they should 'tick' actually.

    It sounds like you have no lash. A valve is staying open slightly.

  8. #8
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    If you want solid help, give full sentence replies and be detailed, or this will get out of hand quickly and it will never run...

    Also one more question.

    How many 4 stroke topends have you rebuilt?

  9. #9
    Join Date
    Jul 2018
    Location
    PA
    --
    29
    Alright. Have not rebuilt any top ends ever 100% new to this. Sorry, Im trying my best to rely information without dragging on with everything i have already done. Im pulling the motor off now and going to check everything over again. By setting the valve clearance i used the valve adjuster tool and tightened it slightly so it barely has clearance(so shaking it a bit it does not tick), maybe a valve is staying closed or that is too tight. Its tough to get a feeler gauge in there and im pretty sure all my other timing is set properly and will be when i reassemble

  10. #10
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    Pictures of your cam timing would be helpful. Pictures of everything always helps with diagnosis. Even if it's "just a 200 motor", it puts us there with you and makes it so much easier.

    There are some people that can set valve clearances by feel, but they have a lot of experience.

    You generally have to bend the end of your feeler gauges to get accurate readings on these engines. As you said, there's not much room.

    Just some info while it's in my brain. Your engine has to be at TDC on the compression stroke to set the valve clearance. As you turn the flywheel, watch the intake rocker arm go down, come back up, and just as it gets to the point of rest, start watching your timing marks. It has a tendency to want to keep rolling past tdc on the "T" mark, so be mindful. Don't rotate 4 strokes backwards. If you roll past TDC, you need to keep going back around until you reach it again. Sometimes friction resistance on the flywheel is a good way to keep it from rolling over.

  11. #11
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    PS those valve adjuster tools suck. It is very easy to unknowingly over tighten an adjuster if you don't have much experience, and that makes it so a valve stays open. If you have no ticking when you grab the rocker and move it, then you have zero lash, and that is bad.

  12. #12
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    Also do not pour oil into your cylinder because if you just honed the barrel for new rings you don't wanna do that. The very last thing you want is excess oil in your cylinder the first time it starts. The rings will never, ever seal.

  13. #13
    Join Date
    Jul 2018
    Location
    PA
    --
    29
    Okay thanks for the input i will upload some photos. I know im not that experienced with these small motors thats why its quite frustrating when i think im doing everything correct but there is definitely some major thing i am missing. Either my valves are in bad condition.... My timing is super off from the valve clearance ( or would the timing chain slipping off mess that up? ).... or there's some crack or something somewhere im not noticing which i highly doubt. I grabbed this thing on craigslist for cheap to try and get it running again but my little knowledge has made it cost me more than it probably should to even get it running. When i first got it it would roll start down the hill but run awfully and not idle well never really got to really ride it, eventually didnt start back up one day at all so thats why i went through the electrical system first thinking it was spark related.

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  14. #14
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    Jul 2018
    Location
    PA
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  15. #15
    Join Date
    Mar 2019
    Location
    Missouri
    --
    35
    Probably needed a carb clean. Lol.

    Post pictures of your cam timing.

    Your valve clearance has nothing to do with mechanical or spark timing.

    You shouldn't be taking it all apart again you should just be checking the valve clearance at this point.

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